For the light source from a light-emitting diode (LED) to be well diffused, a general LED lamp usually includes a lens disposed in front of the LED, so that the light source from the LED is projected through and refracted by the lens to form an illuminated area at a desired location. A conventional lens for this purpose has only one concave surface. Therefore, the light source passed through the lens is diffused at a uniform angle, and a significant halo is formed around the illuminated area. The light source passed through the conventional lens is not soft enough to thereby easily cause sore eyes when a user works under the LED lamp over a long time. The sharp light also tends to result in poor sight. It is therefore tried by the inventor to develop an improved light source lens that may be applied on an LED lamp to concentrate the light source while creating a softer lighting effect, so as to eliminate the above-mentioned disadvantages.